Thoughts on bronze vs. iron vs. steel gibs.

[AndySomogyi]

This is the original top slide gib out of a Clausing 5400. It is made of some sort of mild steel. Not the best bearing material.

As you can tell, it is damaged. I’ve already straightened it out some, and still have a ways to go straightening it.

I’m thinking about making a new one from bronze. I know bronze is a much better bearing material, because bronze is naturally porous and retains oil. Bronze tends to just wear, whereas steel tends to gum up into itself.

So, what are your thoughts on making a new bronze gib?

From what I’ve seen, bronze gibs don’t seem very common, what do you suppose is the reason for that?

 

[Ulma Doctor]

gibs are often made from cast iron for many reasons, one being longevity, a second reason is low cost to cast, and third- easy to machine
they have proven their utility and strength.

bronze gibs can be very useful, but may wear faster dependent on what grade of bronze is selected
certain bronze flavors are harder than steel and would last forever, but they may wear the parts they were designed to be the wear part for.

think of a gib as a sacrificial adjustment member.
as it wears, often it can be drawn or pushed into its socket further, reducing the clearance between the gib and the sliding member.
if the gib is too hard, the sliding members may wear at an accelerated rate
if the gib is too soft, it will wear quickly, but doesn't pose as much of adverse wear effect on the sliding members, but may require constant adjustment to keep clearances from feeling too loose.

i wish you the best of luck, whichever material you may choose

 

[AndySomogyi]

gibs are often made from cast iron for many reasons, one being longevity, a second reason is low cost to cast, and third- easy to machine
they have proven their utility and strength.

bronze gibs can be very useful, but may wear faster dependent on what grade of bronze is selected
certain bronze flavors are harder than steel and would last forever, but they may wear the parts they were designed to be the wear part for.

think of a gib as a sacrificial adjustment member.
as it wears, often it can be drawn or pushed into its socket further, reducing the clearance between the gib and the sliding member.
if the gib is too hard, the sliding members may wear at an accelerated rated
if the gib is too soft, it will wear quickly, but doesn't pose as much of adverse wear effect on the sliding members, but may require constant adjustment to keep clearances from feeling too loose.

i wish you the best of luck, whichever material you may choose

Cast iron makes a lot of sense for gibs, it’s an excellent bearing material, and is cheap and easy to machine, and reasonably strong and durable.

I did find it pretty strange that the factory put in steel gibs, because the steel is definitely harder than the cast iron ways. There is some obvious wear on the cast iron dovetail from where the steel gib was contacting it.

Steel on steel is the worst bearing ever. Had a friend insist on making a steel bushing over steel pin bearing for a dump truck. Ha ha, was completely destroyed after 6 months.

Well, at least here in this lathe, it’s dissimilar metals. I think what really destroys like-metal bearings, is bits wear off and bind to the opposite side, which just accelerates wear. But with dissimilar metals, worn bits tend to flush out of the bearing assembly.

Anyway, short term, I think I’ll just straighten this one out and sand / scrape it flat, get it working, and might revisit it with a bronze gib later.

because this is such a thin flat gib, I don’t think cast iron would work well, I think it would likely crack quickly. Not sure though.

 

[mikey]

Sherline uses a molded composite plastic for their gibs and when I bought it 30+ years ago I remember people laughing and poking fun at the toy gibs used in the toy machines. Sherline claimed the gibs would essentially last forever and folks laughed even harder. The gibs ride on anodized aluminum on one side and steel on the other. In the last 30+ years, I have never had a gib wear significantly and I've only ever had to adjust them maybe once. I lubed them once or twice in all this time and still no wear of any significance and this is on a lathe and mill that has taken cuts much larger than many machines that are much larger than they are.

The gibs on my Emco lathe and RF-31 mill are cast iron but if they ever wear to the point that I have to replace them, I think I'll look into a plastic composite material that I can machine to the proper shape and give it a try. I just cannot argue with success.

 

[benmychree]

Wear on a compound rest gib is not worth worrying about, there is so little motion involved ----- Straighten it, scrape it to fit and have done with it.

 

[RJSakowski]

Bronze is not porous by nature. Oil filled bronze is made by sintering bronze powder. Machining oil filled bronze can fill the pores in the surface, reducing the effectiveness of the bearing so special precautions should be taken. Abrasive procedures should be avoided due to the potential for embedding abrasive particles in the bearing surface.

Tooling should be razor sharp and if a cutting lubricant is used, it should be the same as the oil impregnation. If any heat has been generated causing loss of oil during the machining process, the bearing should be impregnated again. I do this by heating the bearing to drive out any entrained air and soaking the bearing in oil.

In the wild, it would be unlikely that any cutoffs, drops, etc. are oil filled and I wouldn't assume they were unless the identity was known. A test for oil filled bronze is to wipe the surface dry heat it. Oil filled bronze will ooze oil. Oil filled bronze is available from McMaster Carr in various forms.

 

[AndySomogyi]

Sherline uses a molded composite plastic for their gibs and when I bought it 30+ years ago I remember people laughing and poking fun at the toy gibs used in the toy machines. Sherline claimed the gibs would essentially last forever and folks laughed even harder. The gibs ride on anodized aluminum on one side and steel on the other. In the last 30+ years, I have never had a gib wear significantly and I've only ever had to adjust them maybe once. I lubed them once or twice in all this time and still no wear of any significance and this is on a lathe and mill that has taken cuts much larger than many machines that are much larger than they are.

The gibs on my Emco lathe and RF-31 mill are cast iron but if they ever wear to the point that I have to replace them, I think I'll look into a plastic composite material that I can machine to the proper shape and give it a try. I just cannot argue with success.

I don’t think you can just replace cast iron gibs with composite. From a friction surface, I’m sure it would be fine. But there are a lot of mechanical properties of the gib that have to be taken into account. Like with a tapered gib, they’re under a lot of compression, not sure how well composite would work.

Basically what I’m trying to say some machines I known have composite wear surfaces (Hardinge), but the composite is bonded to a metal surface to give it the required mechanical properties.

Anyways, I spent a bit of time straightening out the original gib, and honed it flat, gave it a bit of a polishing. I might also give it a few scrape passes, but I’m pretty happy with it as-is.

In the future, I might experiment with a bronze gib, but I think this factory steel gib is good enough for now.